wpf DrawingContext 绘图方式

1.继承UIElement,重写OnRender方法

public partial class Window5 : Window{    public Window5()    {        InitializeComponent();        this.Content = new RectangleElement();    }}public class RectangleElement : UIElement{    protected override void OnRender(DrawingContext drawingContext)    {        drawingContext.DrawRectangle(Brushes.Red, null, new Rect(0, 0, 100, 20));        base.OnRender(drawingContext);    }}

2.DrawingVisual 轻量级绘图，只提供显示和测试点击功能,DrawingVisual继承自ContainerVisual,所以其也是Visual集合容器

public class RectangleElement : UIElement{    DrawingVisual visual;     public RectangleElement()    {        visual = new DrawingVisual();        var drawingContext = visual.RenderOpen();        drawingContext.DrawRectangle(Brushes.Red, null, new Rect(0, 0, 100, 20));        drawingContext.Close();        this.AddVisualChild(visual);    }    protected override Visual GetVisualChild(int index)    {        return visual;    }    protected override int VisualChildrenCount    {        get        {            return 1;        }    }}

DrawingVisual无法单独存在,必须放在一个容器中(需要有布局系统)呈现.我们看到每次添加一个Visual的时候,总还是难免要实现GetVisualChild和VisualChildrenCount这两个成员.除了ContainerVisual这些轻量级的对象,Panel会帮我们做掉上面这些工作.但基类却变成了UIElement.事实上当添加Visual以后,同时还要计算布局的尺寸,所以有必要的话，可以对UIElement或者FrameworkElement重写以上两个成员。因为有时候我们只需要一次布局和添加多个Visual,以提升性能

重写默认窗体的视觉树

public partial class Window5 : Window{    DrawingVisual dv;    public Window5()    {        InitializeComponent();        dv = new DrawingVisual();    }    protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo)    {        var drawingContext = dv.RenderOpen();        drawingContext.DrawRectangle(Brushes.Red, null, new Rect(0, 0, this.ActualWidth, ActualHeight));        drawingContext.Close();        base.OnRenderSizeChanged(sizeInfo);    }    protected override Visual GetVisualChild(int index)    {        return dv;    }}